Complexities of Antimicrobial Use in Livestock and Poultry Production

10/11/2016 4:13:09 PM

Christine B. Navarre

Antimicrobial resistance is considered by many to be the most complex problem facing public health today. Human health, animal health and the environment are all interrelated, and much is still unknown about the role each plays in antimicrobial resistance. This, unfortunately, leads to speculation, misinterpretation and misuse of the available information. What has followed is intense scrutiny of the use of antimicrobials in livestock and poultry production in the past decade. Antimicrobials are used to combat bacteria, fungi, viruses and parasites.

A concern is that if a food animal harbors an antimicrobial-resistant organism, the potential exists for that resistance to spread to people through the food supply. While this is plausible, the evidence to support human foodborne illness from a resistant organism arising from antimicrobial use in food animals is sketchy. Even if resistance from use in food animals should make it to food products, properly cooking food should prevent illness and spreading resistance.

Other commonly cited concerns are the amount of antimicrobials used in food animals as well as the indication for use. Anti-animal agriculture activists commonly report that 80 percent of antimicrobials in the U.S. are used in food animals. This number is misleading for several reasons, but the main one is that this figure includes a class of antimicrobials that even opponents agree has no impact on human health. Also, pounds of food animals outnumber pounds of people approximately 2 to 1, so it is expected that use in animals would be higher than in people.

The indications for use of antimicrobials in food animals are also often misunderstood. The terms “non-therapeutic” and “sub-therapeutic” are often used, but they have not official definition. The U.S. Food and Drug Administration approves four general uses: to increase rate of gain or feed efficiency, for prevention, for control, and for therapy/treatment.

It is common for opponents to implicate the use of low doses of antimicrobials delivered in feed to large groups of food animals for growth promotion and prevention as contributing to widespread antimicrobial resistance. The fact that bacteria don’t behave according to label classifications, and sweeping generalizations such as this are not based on science. Each bacteria-animal-antimicrobial-dose-delivery combination is unique, and extrapolations should not be made from one combination to another.

Central to this debate is the application of the Precautionary Principle – which means when an activity raises threats of harm to human health or the environment, precautionary measures should be taken, even if some cause-and-effect relationships are not fully established scientifically. In this context, the use of the Precautionary Principle would dictate that antimicrobial use in food animals should be banned just because a threat is possible, even though risk assessments show that this use poses a miniscule risk to human health. Unfortunately, applying the Precautionary Principle has potential downsides. Using these products makes animal food production more efficient, making food more available and more affordable with less impact on the environment. Some risk assessments show a possible increase in food-borne illness. Also, there are animal welfare implications to withholding medications from animals in need.

While there is much still to learn about antimicrobial resistance, most public health professionals will agree on some general principles:

– Antimicrobial resistance is a worldwide problem for both humans and animals. Animals can transfer resistant bacteria to people, and people can transfer resistant bacteria to animals.

– Any antimicrobial use in animals, people or the environment can potentially lead to resistance. Antimicrobial resistance can also arise without the use of antimicrobials.

– While antimicrobial resistance is biologically inevitable, it is everyone’s responsibility to try to slow down the progression to preserve uses for as long as possible.

– Prudent use of antimicrobials in people, animals and the environment is essential. What is in debate is what constitutes prudent use.

To address the rising concern of antimicrobial resistance, the Food and Drug Administration in 2003 issued Guidance for Industry (GFI) #152, which describes a risk-based assessment process to evaluate the potential for antimicrobial resistance to be used in the approval process for new antimicrobial drugs in food-producing animals.

In 2012, FDA followed with GFI #209, which includes two key principles:

– The use of medically important antimicrobial drugs in food- producing animals should be limited to those uses considered necessary for ensuring animal health.

– The use of medically important antimicrobial drugs in food-producing animals should be limited to those uses that include veterinary oversight or consultation.

This was followed in 2013 by GFI #213, which gives more specifics on implementing the principles of GFI #209. It defines “medically important” and lays out a process and data requirements for updating product labels. Medically important antimicrobials in food animals for use in feed and water:

– Can no longer be used for growth promotion or feed efficiency.

– Can no longer be acquired over the counter.

– Require veterinary oversight. Feed uses require a Veterinary Feed Directive (VFD), and water uses a require a prescription

These requirements go into effect January 1, 2017. A livestock or poultry producer will need a VFD order, which is like a prescription, from a veterinarian to buy a fee or mineral containing a VFD drug. Some drugs will no longer be available over the counter including chlortetracycline for use in feed, drugs or anaplasmosis control; medicated milk replacer; and feed and water antibiotics for poultry. By law, a veterinarian and a livestock producer must have a relationship called a Veterinary Client Patient Relationship (VCPR) to issue a VFD or a prescription. The VCPR is defined in state veterinary practice acts and in federal law. Veterinarians will need time to become familiar with a livestock operation before they can legally establish a VCPR. Producers who do not already have a relationship established with a veterinarian should do so now so they are ready.

For more information from the LSU AgCenter, go to Animal Health for a listing of helpful publications.

The American Veterinary Medical Association has a fact sheet on Antimicrobial Use and Antimicrobial Resistance FAQ.

More information about the Veterinary Feed Directive, go to the Food Animal Residue Avoidance Databank.

The National Institute for Animal Agriculture has a listing of White Papers.

Christine B. Navarre is the LSU AgCenter extension veterinarian.

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